Encyclopaedia Index


------- PIL real; default = 1005.0; group 9


CP1 is a PIL variable used for specifying the specific heat at constant pressure of the phase-1 material. It is employed within PHOENICS for deducing temperature from enthalpy, or vice versa.

The text-book definition of specific heat is that it is the rate of change of enthalpy with temperature; but PHOENICS makes use of a non-standard definition described here.

The difference of definition is important only when specific heat varies with temperature.

The default value of CP1 is that pertaining to air at standard pressure and temperature.

Setting CP1 by way of the Q1 file

As is true of all material properties used by PHOENICS, there are several ways of prescribing the value of the specific heat which is to be used at each location and time.


  1. Setting CP1 in the Q1 file to a positive value dictates that it is that constant value which must be used during the calculation.

  2. Alternatively, setting CP1 to GRND1, 2 etc indicates that a formula coded in GXSPEHE is to be used.

  3. If, however, the Q1 file contains the command STORE(CP1) or STORE(SPH1) the specific heat which is used will be that which is ascribed, cell-by-cell, to the corresponding 3D-stored variable.

    Such values can be prescribed in the usual ways, namely via:

    1. In-Form,
    2. the use of FIINIT and INIVAL patches,
    3. settings of the material-indicating variable PRPS, or
    4. creation of GROUND coding via PLANT or otherwise.

It is Method 2 i,e, the use of the built-in formulae, which will now be described.

In these formulae, the absolute temperature, Tabs, is equal to the local temperature, TEM1, plus the constant, TEMP0, which is set in the Q1 file.

It should be remarked that the built-in formulae are rather unsophisticated. Users are recommended to use the In-Form method for introducing specific-heat information of any complexity.

The built-in formulae

Other topics

If STORE(CP1) or STORE(SPH1) appears in Q1, then the specific heat will be placed in a 3D store and will be available for printing in RESULT and plotting with PHOTON from PHI.

In GROUND, the integer index ISPH1 should be used in calls to FN routines or as the argument of L0F.

See also PHENC entries, SPECIFIC HEATS and TEM1.